1. Resistance Resistance is a natural feature of materials.
Metals are good conductors and non-metals are usually insulators.
Most conductors follow Ohm’s law (I=V/R) where R is the same constant at any voltage. Voltage dependent resistors (VDR) are non-linear components, where R changes when voltage changes. VDRs can be used e.g. in over-voltage protectors.
The resistance depends on the length l and area A of the conductor and the resistivity ρ of the material:
Picture from Wikipedia

2. Typical resistivities
Material
Resistivity
Silver
1,64 E-8
Nichrome
100E-8
Copper
1,72E-8
Silicon
2500
Aluminium
2,83E-8
Paper
10E10
Iron
12,3E-8
Mica
5E11
Constantan
49E-8
Quarz
1E17
In temperature dependent resistors (NTC or PTC resistors) the resistance
changes, when the temperature changes. They can be used for measuring the
temperature or for limiting the current of a circuit in overload situations.
PTC (Positive Temperature Coefficient) cables can be used as self-regulating
heating cables. The heating power decreases automatically when temperature rises.

3. Ohm’s law and Kirchhoff’s laws
The voltages and currents in a circuit containing resistors and voltage or current sources can be calculated by using Ohm’s law (I =V/R) and Kirchhoff’s laws (two laws in the picture, but which two …)
For some cases there are simple calculation formulas, which are based on these basic laws. Examples of this kind of rules (on next slide) are
resistors in parallel
resistors in series or
voltage division using resistors.
Ohm’s law and Kirchhoff’s laws

4. Resistors in parallel and in series
Voltage divider:
Vout = Vin * Z2 /(Z1 + Z2)

5. Capacitors Capacitors are components that can store charge.
The capacitance C tells how much charge Q is in the capacitor, when the voltage over the capacitor is V.
Parallel-plate capacitor is the simplest type of capacitor. The capacitance C of parallel-plate capacitor can be calculated from the permittivity of the insulating material  = 0 r , area A and distance d between the plates.
Some dielectric materials like ceramic materials, tantalum oxide or aluminium oxide have a high value of relative permittivity r . These materials can be used as an insulation for capacitors that have a big capacitance in small size.
Capacitance can be made higher by using thinner insulation (smaller value of d), but this makes the breakdown voltage of the capacitor smaller.
Picture from Wikipedia

6. Capacitors in parallel and in series (Note: For parallel capacitors the capacitances are added. But for resistors and inductors the opposite is true: For serial resistors or inductors the resistance or inductane values are added.)
The unit of inductance is
As/V. It is called Farad,
but usual values are
micro- or nanoFarads…

7. There are many types of capacitors
Pictures from Wikipedia
Big aluminium electrolyte capacitor
Tantalum capacitors
Capacitors in the picture below
(from left to right):
Multilayer ceramic
Ceramic disk
Multilayer polyester film
Tubular ceramic
Polystyrene
Metallized polyester film
Small aluminium electrolyte

8. Aluminium electrolyte capacitors
In this picture
you can see
an exploded
electrolytic
capacitor.
Aluminium electrolyte capacitors
Cylindrical shape and big size
They are polarized: DC voltage must be connected to correct direction. Otherwise the capacitor may be damaged or even explode. (There is a + or – sign close to one of the terminals.)
Typical values are big, e.g. 100 nF to 4700μF. Used in power supply circuits in order to keep the output voltage stable.
Typical maximum voltage values 12V,16V, 32V, 64V (but can be even hundreds of Volts).
Made of long sheet of aluminium that is coated by a very thin layer of aluminium oxide. The capacitance can be very high, because the insulating oxide layer is very thin (small d) and has a high value of r
The electrical connection to the other capacitor terminal happens through a conducting liquid (electrolyte).
Pictures from Wikipedia

9. Tantalum capacitors Low voltage devices
Smaller mechanical size than in aluminium electrolyte capacitors
Capacitances 1μF – 150μF
Stable capacitance and very low impedance in low frequencies
Dont like voltage spikes
They are polarized: DC voltage must be connected to correct direction. (There is a + or – sign close to one of the terminals.) Can explode if connected to the opposite direction.
Picture from Wikipedia

10. Plastics capacitors Picture from Wikipedia
Typical materials polystyrene, polyester, polypropylene or teflon
The insulation is plastics foil.
Some plastics capacitors are mechanically very small, because they use very thin foils. These capacitors are for low voltages only.
Other plastics capacitors are mechanically bigger, because they use thicker foils. These capacitors can be used for higher voltages, too.
Capacitance values are small or medium (1 nF – 50μF), but the eletrical values are good and stable. These are good capacitors for small-signal electronics. For example operational amplifier circuits like active filters, integrators and differentiators use most often plastics foil capacitors.

11. Ceramic and mica capacitors
Ceramic insulation materials can have a high value of permittivity, which makes it possible to make capacitors that have very small mechanical size but still a reasonably high capacitance value. Many ceramic capacitors can also be used at high voltages.
Signal conditioning ceramic capacitors at the higher left
corner (and some tantalum
and one small electrolyte capacitor):
In the tantalum capacitors
you can see that maximum
voltages are small (e.g. 20V
or 16V or 10V). The polarity
is marked with + or – sign
at one end.
Picture from Wikipedia

12. Coils or Inductors
The DC current through a coil creates a magnetic field.
A coil is a short circuit for DC. Low frequency currents go easily through inductors, but high frequency currents are attenuated or completely blocked.
Series and parallel connections are calculated as in resistors.
The voltage v of the inductor L is proportional to the rate of increasing (or decreasing) the current i:
The inductor stores in its magnetic field an energy that is proportional to the square to the current. It is not possible to increase (or decrease) the current of the inductor without bringing more energy to (or taking away some energy from) the inductor.
The unit of inductance is
Vs/A. It is called Henry,
but usual values are
milli- or microHenrys…

13. Resistance resists current
Resistance resists current. Inductance makes it more difficult to decrease or increase the current. Big capacitance means that a lot of current is needed for changing the the voltage.
The 2nd man in the picture cannot stop eating. A circuit with big inductance cannot stop (or start) the current before enough energy is taken away from (or brought to) the circuit.
The 3rd man can eat a lot without feeling tension (”too high voltage”) in his stomach. Big capacitance makes it more difficult to change the voltage accross the capacitor. A lot of current must be fed to a big capacitor to increase its voltage.

14. Hydraulic analogy of C, L and R
Pictures from Wikipedia
In the hydraulic analogy, a capacitor is analogous to a rubber membrane sealed inside a pipe. The membrane stops continuous flow to one direction (DC), but it allows short time flow that is changing direction often (like AC). The membrane is repeatedly stretched and un-stretched by the flow of water, which is analogous to a capacitor being repeatedly charged and discharged by the flow of charge.
In the same analogy, an inductor is analogous to a heavy paddle wheel rotating in the flow (or a liquid that has a high mass). It is difficult to make it moving, but it is also difficult to stop it.
The resistor is analogous to a very narrow pipe that resists the flow.

15. Transformers
When two coils are put close to each other  by mutual inductance the energy is transferred from one coil to the other. If the coils have different number of turns (N), the transformer can make the voltage higher and the current smaller (or voltage smaller and current higher):
VP / VS = NP / NS IP / IS = NS / NP
Picture from Wikipedia

16. RLC-circuits as filters
RLC-circuits can be used as filters:
High-frequency current can easily
go through a capacitor. Low-frequency
or DC currents are stopped by the
capacitor.
Low-frequency or DC currents can easily
go through an inductor. High-frequency
currents are stopped by the inductor.
RLC-circuits are called passive filters.
In electronics we usually prefer active
RC-filters that consist of operational
amplifiers, resistors and capacitors but
no inductors (because inductors are big
components and sensitive to magnetic interference).

17. Material types Conductors (resistivity about 10E-7 Ωm) Insulators
Semi-conductive materials (resistivity over 1010Ωm)
Germanium was the material of the first transistors.
Silicon has replaced germanium in modern electronics.
Compound semiconductors (GaAs) are used e.g. in optical components like LEDs.
The fabrication process can chemically change different parts of the semiconductor component into a different type:
P-type semiconductors (holes are the majority current carriers)
N-type semiconductors (electrons are the majority current carriers)

18. Diodes P-type end is anode and n-type is cathode
Current is possible only in one direction.
AC-current will be rectified by a diode, because the current in opposite direction is not possible. The rectified half-sinusoid pulses can be filtered into DC current by using big capacitors.
Voltage-stabilizing circuits use special diodes, that conduct also to the opposite directions at a certain voltage. This voltage over zener-diode does not depend on the current passing the component.
Light emitting diodes (LED) work like diodes, but when they have a current, part of the power is released as light. In most other components the power lost in the component is turned into heat.

19. NPN and PNP transistors
Transistor is a current controlled current source. The bipolar NPN transistor has two n-type areas and a thin p-type area between them. In PNP transistors there are two p-type areas and one n-type area.
The transistor can be used as a switch or as an amplifier.
There is also a second group of transistors. They are FETs (Field-effect transistors) which are voltage-controlled current sources.

20. Integrated circuits (ICs)
ICs include many integrated components, especially transistors
SSI small-scale integrated ICs (operational amplifiers, voltage regulators, basic digital circuits) have tens of transistors in one IC. This technology is about 50 years old but some SSI components are still commonly used.
MSI (medium scale integration) had hundreds of transistors in one IC
LSI (large scale integration) had thousands of transistors in one IC. For example the first microprocessors 40 years ago were LSI circuits.
VLSI (very large scale integration) has at least tens of thousands of transistors in each IC, but many todays digital ICs like microprocessors or memories have hundreds of millions of transistors.
The use of ICs can make the design on electronic circuits much easier than the design of circuits using separate (discrete) transistors. Especially in analog electronics the operational amplifier ICs are used a lot.

21. Operational amplifiers (OpAmps)
OpAMPs are used to amplify or process analog signals in e.g.
Filtering circuits
Summing or subtracting of analog signals
Integrators and differentiators
The basic idea of OpAmp is very high amplification (gain) and the use of negative feedback. The OpAmp has two inputs. The output voltage is the difference of the input voltages multiplied with the gain.
The gain is an extremely big number, e.g or We can simplify calculations by thinking that the gain is infinite.

22. Negative feedback in OpAmp circuits
Negative feedback is created to an OpAmp circuit by connecting a resistor (or sometimes a capacitor) between the output and the inverting input (-).
The negative feedback can be used to set the gain of an OpAmp circuit to the wanted level (see the circuits and gain formulas on the next slides).
The negative feedback also creates a situation, where both inputs (+) and (-) have almost the same voltage. (If these voltages were different, the output voltage should be infinite.) This fact is used in many simplified OpAmp calculations.
An exemption to the above rule is the situation, where the OpAmp cannot give enough voltage or current. In that case the output voltage is smaller than the theoretical value and the input voltages are not equal.
For many OpAmps the highest possible output voltage is about 1 or 2 volts smaller than the supply voltage. (about +14 V if supply voltage is +15 V)
The highest possible output current can be e.g. 20 mA or 50 mA. This means that the resistors loading the output should be typically kilo-ohms. OpAmps are used for signal processing. They cannot be used as power amplifiers for driving e.g. motors or loudspeakers.
The input current of the OpAmp is very small. It can usually be considered to be practically 0. This fact can also be used for simplifying the calculations.

23. Inverting amplifier If you want to make the gain a positive number,
you can add a second amplifier, where Rf=R1
The input current that is taken from vin is not 0. It flows first through R1 and then through Rf to the output of the amplifier.
The negative feedback makes both OpAmp inputs to have equal voltage. Also the inverting input (-) must have a voltage of 0 V. It is called a virtual ground.

24. Non-inverting amplifier
The gain a positive number. It is always bigger that 1.
The input current that is taken from vin is practically 0. This means that the amplifier has a very high input impedance.

25. Unity-gain buffer
If the feedback resistor of an non-inverting amplifier is replaced with a short-circuit (Rf=0), the gain will be G=1. (The R1 can now have any value, and so we can also leave it away.)
This unity-gain amplifier has a very high input impedance, because the input current is practically 0. This circuit can be used as a buffer amplifier. It prevents the voltage drop that usually happens, when a load is connected to a transducer. (Compare to Electronics assignments 3: task 4)

26. Inverting summing amplifier, DAC-
The gain is always a negative number. If you want to make the gain a positive number, you can add an inverting amplifier, where Rf=R1
The input currents that are taken from v inputs are not 0. All these currents go through Rf and create a voltage that is proportional to the sum of the currents.
In simplest case all the resistors have equal values and the output is a usual sum. By using different resistors, the inputs can have different weights. Compare to the Summing amplifier DAC in

27. Differential amplifier
If all resistors are equal, the output voltage is simply V2 – V1
Differential amplifiers are used in signal processing.
In instrumentation systems electronic signals are often transmitted in long wires as a difference of two voltages. This method can cancel interfering voltages.

28. Integrator

29. Differentiator (derivative amplifier)

30. Comparator, AD-converters
Comparator is an OpAmp without negative feedback. There are only two possible values for the output voltage: either its maximum value or minimum value. Typical values are 1 or 2 volts below the supply voltage.
If supply voltages are +15 V, the comparator works like this:
Vout = +14 V if V1 > V2 Vout = -14 V if V2 > V1
The output signal can be considered as a digital signal (binary signal), because it has only two levels.
Comparators can e.g. be used for switching the heating ON or OFF depending on the voltage of a temperature transducer.
Analog signals can be represented as digital numbers by using Analog-to-Digital converters like the Flash ADC in
Flash ADC is a simple and fast circuit, but it requires a big number of comparators, if many comparison levels (many different possible numbers) are needed. There are other ADC principles that need less comparators, but more digital circuits.

31. Comparator with Hysteresis
As mentioned earlier, a comparator can be used for switching some equipment (e.g. a heating resistor) ON or OFF depending on a voltage (that is measured e.g. from a temperature transducer).
This simple circuit causes a practical problem. The heating can be switched all the time between ON and OFF. This can damage the switching component and causes unnecessary electric interference.
The problem can be solved by using a comparator with positive feedback. The positive feedback changes the voltage level at the other input of the comparator. Switching from low to high happens at different voltage than switching from high to low. This is called a hysteresis.
E.g. the heating could be swithed ON when temperature drops under +20 C and switched OFF when temperature rises above +21 C.
Electronics assignment 6 is an example of a comparator with hysteresis, which is based on positive feedback.